Current barrels 1, as illustrated in FIG. 1, are generally formed by a box 3 called a “drum” intended to receive a pivot arbour 5 and a spring 7. Spiral spring 7 has a length L, a height H and thickness E. Spring 7 is mounted between the internal wall of box 3 and the external wall of pivot arbour 5. Box 3 is generally closed by a cover 9. Spring 7 can thus be wound to supply mechanical energy to the movement of the timepiece in which it is integrated.
The problem raised by this configuration of current springs is that a constant torque is not provided throughout the entire letting down of said springs, which causes a variation in the amplitude of the balance detrimental to the precision of the timepiece movement.
Moreover, it is difficult to reconcile the shape of current substantially S-shaped springs at rest and the space required thereby with positive fabrication, i.e. photolithography followed by electroforming, or negative fabrication, i.e. photolithography followed by etching. Indeed, the substrates used are not large enough and/or an insufficient number of springs are made on a single substrate making production costs unacceptable.